Zusammenfassung
The Palmyride fold belt is a northeast-trending, 400 by 100 km transpressive
belt in central Syria embedded in the northern Arabian platform,
bounded to the north by the Aleppo plateau and to the south by the
Rutbah uplift. Palinspastically restored cross sections from three
transects across the Palmyride fold belt demonstrate a minimum NW-SE
shortening of about 20\% or 20 km across the southwestern segment
of the belt, diminishing to 1-2 km in the northeast, close to the
Euphrates graben system. The cross sections are based on the 1:200,000
scale geologic map of Syria and previously unavailable seismic reflection
and well data, all provided by the Syrian Petroleum Company. These
results differ significantly from those predicted by kinematic models
of Middle East plate motions. In western Syria and eastern Lebanon
the Palmyrides obliquely intersect (at about 45 deg) the roughly
north-trending Dead Sea transform fault system. The Dead Sea fault
system shows well-documented evidence of 105 km of left-lateral displacement
since mid-Tertiary time south of its intersection with the Palmyrides,
yet only about 25 km of motion has been documented north of that
juncture in Lebanon and western Syria. Thus, kinematic models of
Middle East plate motions predict 80 km of shortening in Syria, most
of which should be accommodated in the Palmyride fold belt. Several
possibilities exist to explain the discrepancy between the 80 km
of predicted shortening and the only 20 km of shortening measured
from restored cross sections. Restored cross sections offer only
minimum shortening estimates, so the calculated 20 km may underestimate
shortening. Second, evidence of strike-slip displacement recognized
in minimum shortening estimates, so the calculated 20 km may underestimate
shortening. Second, evidence of strike-slip displacement recognized
in the field and reported in the literature, and indicated by new
focal mechanism solutions of two recent earthquakes in the Palmyrides,
indicates that some of the still 'missing' displacement may be distributed
throughout central and northern Syria as strike-slip motion oblique
to the relative northward convergence of the Arabian plate on the
Eurasian plate. Alternatively, previous estimates of slip along the
northern segment of the Dead Sea transform fault system may be only
minimum estimates. A final possibility is that the Dead Sea transform
fault in northwestern Syria has been active for only the past 5-6
m.y. or so, implying that it was either nonexistent or moved only
slightly before the Pliocene. This would suggest that there is a
total of only 45 km of N-S convergence to be found in central and
northern Syria, about 25 km on the Dead Sea fault system and about
20 km in the Palmyrides. This last possibility requires that the
northern and southern segments of the Dead Sea fault system developed
independently during most of the past 15-20 m.y. In light of the
documented but unquantified strike-slip motion in the Palmyrides,
it seems reasonable that strike-slip motion does accommodate a significant
portion of the convergence between the Arabian and Eurasian plates.
It is likely, however, that one or more of the other proposed mechanisms
also accounts for a component of the expected 80 km of shortening.
Nutzer